Motor drive that is used for railways, electric vehicles, or hybrid vehicles is usually controlled by a power converter (i.e., inverter). For a portion called a main circuit of the inverter, a semiconductor module is used that has mounted thereon a switching element, such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), that controls switching of a large current, and a diode, such as a FWD (Free Wheal Diode), that releases a reverse voltage generated during a switching operation. In the field of vehicles, reductions in the size and weight of the mounted devices have been accelerated. Thus, the power density per device or per package tends to increase. Therefore, it is strongly demanded that insulation against a high voltage be secured and the heat dissipation performance be increased corresponding to the increased power density.
Patent Literature 1 discloses a semiconductor module that includes a set of semiconductor device units obtained by combining a plurality of semiconductor device units each having a sealed semiconductor chip, a wiring substrate, and a bolt fastening unit. Patent Document 1 discloses that an elastic adhesive or an elastic sheet is provided between each semiconductor device unit and the wiring substrate, so that pressure that is applied to the wiring substrate upon fastening of bolts acts equally on each semiconductor device unit, which in turn can improve the degree of contact of each semiconductor device unit with a cooling body as well as the heat dissipation performance.